An improved method for the synthesis of pentafluoroethylated pyridines through Cu-catalyzed[3+3] cyclo-addition reaction of oxime acetates is reported. The starting materials are more readily available, and these reactions occurred under mild conditions with broad substrate scope and excellent regioselectivity. Mechanistic studies have also been preformed.

Organosilicon compounds play an important role in pharmaceutical chemistry, material science and organic synthesis. Transition-metal-catalyzed direct silylation of C-H bond, as one of the most concise and efficient methods for the synthesis of organosilanes, has developed rapidly in recent years. In this paper, the recent advance in transition-metal-catalyzed silylation of C-H bonds since 2015 is mainly reviewed.

A highly convenient and regioselective synthesis of 1,3-disubstituted pyrazoles or 1,3,4-trisubstituted pyrazoles from Cu(Ⅱ)-catalyzed cascade reactions of saturated ketones with hydrazines or aldehyde hydrazones is presented. Mechanistically, the formation of 1,3-disubstituted pyrazoles involves the in situ generation of an enone intermediate followed by its[3+2] annulations with hydrazine. On the other hand, the formation of 1,3,4-trisubstituted pyrazoles is believed to go through a cascade process including enone formation and its subsequent[2+3] annulation with aldehyde hydrazone. Compared with literature methods, the notable features of the protocol include simple starting materials, general and broad substrate scope, high regioselectivity, good efficiency and excellent atom-economy.

Asymmetric cycloaddition reactions catalyzed by Inda-BOX 1 metal complex between two kinds of electron-withdrawing alkenes and C,N-diarylnitrone have been studied respectively. Results showed that the 4-substituted products were mainly obtained in both reactions under the best conditions. When N-acryloyl oxazolidinone was used as dipolarophile, the exo/endo selectivity of the reaction was 100/0, and the ee of the exo product was as high as 97%. When N-acryloyl-3,5-dimethyl pyrazole was used as dipolarophile, the selectivity of exo/endo was 0/100, and the ee of endo product was up to 98%. The relationship of the dipolarophile, the structure of nitrone and the selectivity of the reaction was discussed.

The selective catalytic oxidation of amines for the synthesis of imines is important both in laboratory and industrial production. From atom-efficient, economic and environmental view of points, dioxygen selective oxidation of amines was achieved by using wings-opened butterfly-like complex Cu₂(ophen)₂ as catalyst. It was worth noting that the catalytic system was efficient to the cross-coupling of alcohols with amines, homocoupling of primary amines and oxidative dehydrogenation of secondary amines. The yield is up to 93% and the selectivity of imines is as high as 99%. Avoiding the use of expensive nitroxyl derivatives and base was suitable for practical application.

Due to the lower configuration stability of vinylarenes, arsing from the relatively lower rotational barriers, their catalytic asymmetric synthesis remains a daunting task. Oxindoles moiety are privileged framework of natural products and building blocks of bioactive molecules as well as pharmaceuticals. The asymmetric synthesis of axial chiral vinylarenes fearturing oxindole moiety via sequential carbopalladation/C-H olefination from readily available materials with palladium catalysis has been developed. (4R,5R)-(-)-2,2-Dimethyl-α,α,α',α'-tetraphenyl-1,3-dioxolane-4,5-dimethanol (TADDOL)-derived phosphoramidite gave products with good yield and moderate ee value. The erosion of optical purity was not observed even after heating the product for 10 h at 110℃, which indicates the excellent stability of the chiral axial.

Axially chiral biaryl skeletons are ubiquitous stuctural motifs that are widely represented in pharmaceuticals and natural products, and have been widely used as privileged chiral ligands/catalysts in asymmetric synthesis. Therefore, the asymmetric construction of these compounds has received tremendous attention. However, the established strategies are mainly limited to the construction of biaryls containing hexatomic aromatics, and the approaches towards atropisomers featuring pentatomic heteroaromatics connected through C-C or C-N bond have emerged gradually only until recently. The main hurdle is basically due to the increased distance of substituents ortho to the axis, which is responsible for lower barriers to rotation, thus rendering the asymmetric synthesis more challenging. This review summarizes recent advances on the enantioselective synthesis of atropisomers featuring pentatomic heteroaromatics.

This study describes efficient vicinal dibromination and iodoacetoxylation of olefins under mild reaction conditions. The reaction uses ZnAl-XO₃^--layered double hydroxide (LDHs) (X=Br or I) as an oxidant and LiX as a reductant to generate halogens in situ (ZnAl-XO₃^--LDH/LiX system). A series of dibromoalkanes (74%~95%) and iodoacetates (75%~93%) were obtained in good to excellent yields with high regio-and stereo-selectivity.

A mild method for palladium-catalyzed halogenation of acetanilide with N-chloro-N-fluorobenzenesulfonylamide (CFBSA) as a chlorinating reagent, oxidant, and novel promoting reagent was achieved. The decomposition of byproduct N-fluoroben-zenesulfonylamine in the presence of Pd(OAc)₂ could accelerate the process of chlorination. Preliminary mechanism investigation showed that Pd catalyzed anilide directed C-H activation lead to the ortho chlorination selectivity. A series of ortho-chlorinated anilides were obtained in 28%~82% yields.

The 2-substituted-1,2,3,4-tetrahydroquinoline skeletons are widely found in natural products and have shown antimalarial, antioxidant as well as other biological activities. In this work, MIL-101(Cr)-SO₃H is an efficient heterogeneous catalyst for the transfer hydrogenation of a series of 2-substituted quinoline derivatives with Hantzsch ester as the hydrogen source. This protocol operates under mild conditions, tolerates a wide range of 2-substituted quinoline derivatives, and the catalyst could be recovered and reused four times without considerable loss of catalytic activities, which provides a new catalytic system for the construction of 2-substituted-1,2,3,4-tetrahydroquinoline derivatives.

The chiral Cp ligands as stereocontrolling element of asymmetric catalytic reactions have attracted increasing attention. Particularly, designing and synthesizing more versatile chiral Cp ligands became one of the most interested research focuses in asymmetric catalysis. The complexes of various chiral Cp ligands with different transition metals that advanced in recent years, and the applications of these complexes in catalytic asymmetric reactions are reviewed in this paper.

Alkaline-earth metals continue to receive growing interest, as they are used as low-cost and non-toxic alternatives to transition-metals in various organic transformations. As ionic character and bond lengths increase along the row in the order Mg²⁺2+2+2+, bond energies decrease along the same row, the corresponding metal hydrides are apt to the formation of insoluble metal hydrides[AeH₂]_∞ (Ae=Mg, Ca, Sr, Ba) through Schlenk equilibrium in solution. Recently, a series of alkaline-earth metal hydrides stabilized by suitable ligands were discovered and characterized, and stoichiometric and catalytic reactions with small molecules were studied as well. In this paper, the recent progress in molecular alkaline-earth metal hydrides is reviewed.

Asymmetric hydroformylation is one of the most important reactions for preparation of chiral aldehydes from alkenes. Recently, significant progress has been made in this field and a series of new ligands have been developed. Asymmetric hydroformylation of several important alkenes has been achieved, offering efficient and concise methods for the synthesis of chiral aldehydes. In this review, the achievements of asymmetric hydroformylation of typical alkenes and the development of ligands for asymmetric hydroformylation are summarized.

γ-Hydroxyl or γ-alkoxyl-substituted α,β-unsaturated carbonyls widely exist in a variety of natural products and bioactive molecules. Herein, the realization of 1,4-functionalization of 3-en-1-ynes with alcohols through zinc-catalyzed regioselective N-oxide oxidation is described. This tandem reaction allows the practical synthesis of a range of valuable γ-alkoxyl-substituted-α,β-unsaturated amides in moderate to good yields.

Quinoxalin-2(1H)-ones are very important N-heterocyclic moieties found in natural products and pharmaceuticals, and exhibit an amazingly wide spectrum of biological properties. Numerous efforts have been devoted to the development of efficient approaches for the C-H bond activation and functionalization of quinoxalin-2(1H)-ones in recent years, including alkylation, benzylation, acylation, arylation,amination, amidation, phosphonation, and fluoroalkylation. The recent advances in this area are summarized and their reaction mechanisms are discussed.

A practical method for the oxidation of aromatic side chains was established for the preparation of aromatic aldehydes and ketones. Using NiCl₂ as the catalyst, substituted toluenes were oxidized with Na₂S₂O₈ at the benzylic site for the synthesis of the corresponding aldehydes in the yield of 22%~79%. Ethylbenzene analogs were oxidized more easily to obtain the corresponding ketones with 64%~84% yields. The oxidation of benzyl alcohol analogs was completed to acquire the corresponding carbonyl compounds in shorter time with better selectivity and yields. The method has the advantages such as the mild reaction conditions, no requirement for precious metals or additional promoter, and good selectivity.

The coupling reactions of phenols and nitrogen hetereocycles with aryl halide were catalyzed by a highly active, readily available and easily recoverable heterogeneous Cu catalyst which was prepared by simply stirring an suspension of chitosan in solvent with copper compound. The result showed that chitosan@Cu₂O catalyst catalyzed the coupling reactions of aryl halides with phenols and nitrogen hetereocycles to readily give the corresponding products in moderate to excellent yields. The highly active catalyst can be reused many times without losing its catalytic activity.

Tremendous advance has been achieved for the transition-metal free coupling reactions induced by light these years, providing important strategies for the construction of C-N/S/P bonds, which was used frequently in the preparation of pharmaceutical drugs, agricultural products or materials and so on. In this review, the recent advance for the photo-induced coupling reactions for the construction of C-N/S/P bonds under transition-metal free conditions is reviewed.

The novel biotin conjugated glaucocalyxin A analogs as potential activity-based protein probes were synthesized with good yields via Cu(I) in situ-catalyzed azide-alkyne cycloaddition. Cu(I) in situ was good solvated under the optimized condition and shown high catalytic activity. The approach efficiently constructs the even longer linker containing 1,2,3-triazole nucleus between bifunctional groups with the advantages of high regioselectivity and operational simplicity.

A highly chemo-, regio-, and stereo-selective cobalt-catalyzed dehydrogenative silylation of vinylarenes was described. The imidazoline iminopyridine cobalt complex could promote this reaction effectively and improve the chemoselectivity dramatically. This protocol used earth-abundant transition metal, readily available alkenes and hydrosilanes to construct valuable vinylsilanes. The reaction could be carried out in gramscale and the proposed mechanism was also described.

A green, efficient, and recyclable catalytic protocol for Ullmann C-N reaction in water was developed. The catalyst Chi-Gly@CuI was prepared by the cross-linking reaction of chitosan bead with glyoxal and subsequently anchored with copper salt. Chi-Gly@CuI bead of 0.3 mm in mean diameter possesses porous micro-structure demonstrated by scanning electron microscope (SEM). The structure of Chi-Gly@CuI was characterized by Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TG), X-ray diffraction (XRD), inductively coupled plasma-atomic emission spectrometry (ICP-AES), and X-ray photoelectron spectroscopy (XPS). This catalytic protocol for Ullmann reaction in water exhibited high applicability, from which the corresponding coupling products were afforded in good to excellent yields. Chi-Gly@CuI could be easily separated from products by simple filtration almost without weight loss. Most notably, after 10 times of recycling, its catalytic activity and chemical stability were still maintained.

Heterocyclic compounds are widely applied in medicine, fine chemical engineering and the related industrial fields. Consequently, the development of efficient strategies for heterocycle constructions continues to be of great appeal in organic synthesis. In recent years, the I₂-catalyzed direct C-H bond functionalizations have emerged as one of the most efficient synthetic protocols to construct diverse heterocycles. In this review, the recent advances in I₂-catalyzed C-H bond functionalizations by the types of C-C and C-N/O/S bond formations are summarized, and an outlook of this research filed is given.

A visible-light-induced[3+2] annulation of arylcyclopropylamines and 1,2-diarylethanediones was report. A series of α-amino tetrahydrofuran derivatives were synthesized in moderate to good isolated yields under mild reaction conditions. This method would provide an efficient and convenient approach to α-amino tetrahydrofurans which are potentially important buiding blocks in bioactive compounds.

A metal-free polychloromethylation/cyclization cascade of N-allyl anlines is presented, which provides an access to polychloromethyl-substituted indolines with unactivated alkenes as radical acceptors and dicumyl peroxide (DCP) as the initiator. The inexpensive solvents of polychoromethanes (i.e., CH₂Cl₂, CHCl₃ and CCl₄) were used in the reaction as di-or trichloromethylating agents. This work has advantages of easy operation, mild conditions, low cost, and broad substrate scope.

2-(1'-Acetyl-ferrocenyl) benzothiazole (FcSO) probe was synthesized by the acetylization reaction of 2-ferrocenyl benzothiazole, which was obtained from the cyclization reaction of ferrocenecarboxaldehyde with 2-aminothiophenol. Crystal and molecule structures of FcSO probe were characterized by spectra methods and X-ray single crystal diffraction analysis. The recognition ability to Al³⁺, Cr³⁺, Fe³⁺ ions of FcSO probe was researched by three analytical methods of UV-Vis, fluorescence and electrochemistry. The results show that the recognition to Al³⁺, Cr³⁺, Fe³⁺ ions of FcSO probe is effective via three channels, and the detection limits of FcSO probe to Al³⁺, Cr³⁺, Fe³⁺ ions are 7.456×10^-6, 3.72×10^-6 and 1.35×10^-5 mol/L, respectively. ¹H NMR research results indicate that the acetyl, ferrocenyl and benzothiazole groups of FcSO probe play important roles in recognizing Al³⁺, Cr³⁺, Fe³⁺ ions.

A practical ruthenium-catalyzed C(sp²)-H alkenylation and alkylation of 1-benzyl-1H-pyrazole with alkene or a,β-unsaturated ketones under the assistance of pyrazole group were developed. This method has the advantages of high selectivity, providing only the ortho-alkenylation or ortho-alkylation products in high yields. This protocol provides an efficient and new method for the functionalization of 1-benzyl-1H-pyrazoles.

A series of photothermal cyclobutaosmapentalenes with conjugated groups attached to the metallacycle were synthesized from the reaction of OsCl₂(PPh₃)₃ with an organic multiyne and PPh₃, followed by a[2+2] cycloaddition with terminal alkynes. These highly conjugated metallacycles showed broad UV-Vis absorption and good photothermal efficiency. These easily synthesized metallacycles represent a type of new photothermal material.

Cu(Ⅱ)-promoted C-H nitration of arenes has been disclosed with the aid of N,O-bidentate directing group. The protocol was operationally simple by using NaNO₂as the nitration source. Various amide substrates were tolerated in the reaction system, which establishes opportunities for developing simple and facile methods, and enriches the strategies to access aromatic nitro derivatives.